The maximum price is $200, this includes a mark up of 10%
So the $200 is 110% of the cost.
This means that to find the cost of the unit you have to divide $200 by 110 and multiply by a 100. 200/110 * 100 = 181.82 Or alternatively you have to divide $200 by 1.1 because the selling price includes the 10% mark up.
See if you do it the other way as you would to with a mark-up of 10% 181.8181* 1.1 = $200